Conventional manual transmissions have gearing adapted to establish multiple torque ratios in a driveline for an automotive vehicle. These transmissions typically have two or more shafts, such as a mainshaft and at least one countershaft. Torque delivery gears are mounted for rotation about the mainshaft axis and gear elements are mounted for rotation about the countershaft axis. As the number of possible torque ratios has increased, with many transmissions having five forward speed ratios and one reverse ratio, shaft lengths have increased to accommodate an increased number of gears.
Initially, these long shafts were supported only by their ends. Under the gear loads encountered during rotational gear engagement, these shafts tend to torsionally deflect and bend. This deflection and bending adversely affects proper gear mesh. This contributes to gear tooth wear, gearing inefficiency and gear noise. To solve this problem, some prior art transmissions include a bearing support mounted on the transmission case between the end shaft supports to provide additional shaft support and thus to reduce deflections and stabilizing the shafts. Some of these supports are found in U.S. Pat. Nos. 4,628,768; 2,227,589; and U.S. Pat. No. 1,887,560.
The use of such a center bearing support, however, requires precise alignment between the shaft end supports and the center bearing support. This, in turn, requires machining tolerances of an exacting nature and an impractical, idealized transmission case. In actual practice, shafts supported by a fixed center support and the associated gearing may self-destruct at high speed because of improper alignment.